The present invention relates to a process for the preparation of N-monoallyl-meta-trifluoromethyl aniline which is used extensively as an intermediate in the manufacture of halogenated and N-substituted pyrrolidones.
The preparation of the monoallyl derivative of meta-trifluoromethyl aniline is, for example, an essential step in the synthesis of the herbicide 1-N-meta-trifluoromethylphenyl-3-chloro-4-chloro-methyl-2-pyrrolidone, as described in French Patent No. 2,305,434. However, according to this patent, the preparation of the N-monoallyl-meta-trifluoromethyl aniline intermediate requires allylating a trifluoromethyl aniline in which one of the hydrogen atoms is protected by an acetyl group, in order to prevent the formation of secondary diallylation products which cannot be utilized. Consequently, the process disclosed in this patent takes place in four stages: (1) protection of the amine by acetylation, (2) substitution of the remaining hydrogen by a metal; (3) condensation with an allyl halide; and (4) deacetylation.
However, since multi-stage processes are typically more difficult to implement and less economically advantageous than a single-stage process, the industry has long sought an economical single-stage process for the production of N-monoallyl-meta-trifluoromethyl aniline. Additionally, since meta-trifluoromethyl aniline is a very valuable compound and is desirably conserved, a process is sought which either does not require meta-trifluoromethyl aniline as a starting material or which provides high yields with respect to the meta-trifluoromethyl aniline starting material used.
One solution to this problem is disclosed in U.S. Pat. No. 4,701,560, which describes a single-step process for the allylation of meta-trifluoronethyl aniline comprising reacting an allyl halide, in an aqueous nedium, with a substituted or unsubstituted meta-trifluoronethyl aniline, in the presence of (1) an alkali metal carbonate, an alkali metal hydrogen carbonate or an alkali metal hydroxide, and (2) a catalytic quantity of a tertiary amine. However, in order to produce only small quantities of secondary diallyl products by this method, it is necessary to limit the degree of conversion of the meta-trifluoromethyl aniline by carrying out the reaction in the presence of less than a stoichiometric amount of the allyl halide. For example, the preferred ratio of meta-trifluoromethylaniline to allyl halide is reported to be about 2. Moreover, the yield of the N-monoallylaniline derivative produced, with respect to the meta-trifluoromethyl aniline introduced into the reactor, does not exceed about 40%, which is typically inadequate to obtain good economic profitability from the process.
Accordingly, despite the existence of abundant literature describing the allylation of various anilines, as far as applicants are aware, no process has heretofore been discovered which provides both a high degree of conversion of the starting aniline and a high selectivity for the monosubstituted aniline derivative with respect to the disubstituted aniline derivative.